My money is on the return line along the LH side of the engine. I've seen
them so badly blocked that I couldn't even drill through the crud. You said
the return line was cold with it connected normally, so obviously there is a
blockage between the point where you disconnected it and the front end of
that line (which opens directly into the inlet side of the water pump).
Opening the bypass won't help, as it just provides another path around the
water pump (although I think it is a bad idea to leave the bypass fully
blocked, as you really want some water flowing through the head all the
time).
FWIW, I noticed the other day that Scrappy (the TR3 that Steve Hedke built
to drive in The Great Race) is wearing an oversize round heater that looks
rather similar to the original unit, but sticks down an extra few inches and
has the doors angled to the sides. I have forgotten the details, but it is
sold as a Land Rover part and available from British Pacific. Steve said it
uses a single long tube instead of the many parallel tubes that the original
heater used, and so it is almost impossible for it to get plugged up.
I didn't ask Scrappy's new owner how well it works, but it might be an
option for those of you who are considering an upgrade and want something a
bit closer to "period correct". If you would like more information, contact
Steve at:
British Pacific Ltd.
26007 Huntington Lane, unit 2
Valencia, CA. 91355 USA
tech: 661 257-8634
e-mail: britpac at aol.com
http://www.landroverparts.us
-- Randall
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